The present invention relates to a microscope comprising a main objective having a lens assembly movable in the direction of the optical axis of the main objective for focal length variation and comprising an illuminating unit with illumination deflector means for deflecting an illuminating beam path for generating an illuminating beam path that is directed onto an object plane, the position of the illumination deflector means being adjustable dependent on a focal length variation of the main objective for centering the illumination.
Microscopes of this type are known from DE 195 23 712 C2 and DE 195 37 868 B4. In the first-mentioned DE 195 23 712 C2 a stereomicroscope comprising a main objective with variable focal length, a downstream zoom system and a binocular tube as well as an illuminating unit arranged adjacent to the main objective is disclosed. The main objective comprises a fixed and a movable lens for varying the focal length and the intercept length of the main objective. The fixed, negative lens of the main objective is arranged towards the object plane, the movable, positive lens is arranged behind it (facing away from the object plane). A movement of the movable lens in the direction away from the object plane results in a reduction of the focal length of the main objective. For an optimal illumination of the vertically shifting object plane, it is suggested in this document to adjust the position of an illumination deflector element dependent on a focal length variation of the main objective for centering the illumination. This is done in that the prism lens used as an illumination deflector element is pivoted such that the illuminating beam path tracks the shifted object plane. For this purpose, the prism lens is pivotally mounted about an axis which is perpendicular to a plane that is spanned by the vertical optical axis of the main objective and the illuminating beam path which is incident substantially horizontally inclined on the prism lens. As a result thereof, for all positions of the movable lens of the main objective facing away from the object a focusing of the illuminating light on the respective focal point of the main objective can be guaranteed.
The coupling of the rotary movement of the illumination deflector element with the linear (vertical) movement of the lens of the main objective facing away from the object, as suggested in this document, requires very sensitive rotary movements of the illumination deflector element in relation to the movement of the lens and makes high demands on the mechanical coupling which is designed with a high constructional expense in this document. Any disturbances will be directly visible for the user (particularly given high magnifications). Further, the size of the surface of the deflector element turns out to be disadvantageous, as it has to be sufficiently large in order to cover the entire illuminating pencil even when the illumination deflector element is tilted. Mirrors or the mentioned prism lenses can be used as illumination deflector elements. When mirrors are used, an enlargement of the reflecting surface will result in the additional disadvantage of an increased required thickness of the reflecting surface. Thus, altogether the required space and the height of the weight to be moved are increased.
In the mentioned DE 195 37 868 B4, an illuminating device for a stereomicroscope comprising an objective with a variable image-forming intercept length is disclosed, an illumination intercept length variation being possible via an optical system that is separate from the viewing optical system. Means for coupling the intercept lengths mentioned are disclosed, which means effect that the illumination intercept length and the image-forming intercept length correspond to one another. Further, means for coupling are provided which guarantee that the angular position of a deflector element of the illuminating device is varied such dependent on the respective image-forming intercept length and illumination intercept length that there is always a centered illumination of the viewed field of view. Since, here too, for centering the illumination rotary movements of the illumination deflector elements are performed, here, once again, the disadvantages mentioned occur.
A basically different possibility of illumination centering results when the illumination is guided through the main objective of the microscope. This solution is implemented in the surgical microscope models M520 and M525 of the applicant. Here, the illumination deflector element directs the illuminating beam path to and through the main objective having variable focal length so that the illumination is always centered on the focus.
The microscopes mentioned up to now use vertical zoom systems, i.e. the longitudinal axis of the zoom system lies parallel to the optical axis of the main objective. If, in addition, the illumination is fed into the main objective from above, there will be a high space requirement in vertical direction resulting in microscopes having a relative high overall height in the vertical direction. This is disadvantageous for ergonomic reasons since the distance between the eyepiece and the main objective is increased.
For solving the last-mentioned problem, a stereomicroscope structure has been suggested in the document EP 1 424 582 B1, in which a “lying” zoom system, i.e. a zoom system having its longitudinal axis arranged horizontally, is realized. For this purpose, there is arranged between the main objective and the zoom system a deflector element which deflects the viewing beam path from a substantially vertical direction into a substantially horizontal direction and feeds the same into the zoom system arranged in a first horizontal plane. By means of further deflector elements the viewing beam path exiting the zoom system is deflected into a second horizontal plane which extends substantially parallel to the first horizontal plane and in which optical add-on components are arranged. With respect to details on the structure and the mode of functioning of such a stereomicroscope with “lying” zoom system reference is explicitly made to the mentioned European patent specification.
In this stereomicroscope, the illuminating unit is arranged substantially adjacent to the main objective und below the zoom system, the illuminating beam path being guided outside the main objective. Instead of an illumination centering, it can be ensured by means of a sufficiently large illuminated field that the visual field is always illuminated given a focal length variation of the main objective. Such a generously designed illuminated field requires a correspondingly largely designed illuminating aperture and thus illuminating unit, which in turn has a negative effect on the ergonomics of the microscope. A further disadvantage in this connection is that the homogeneity of the illumination (intensity in the illuminated field) cannot be the same for all positions of the multi-focus (variable focus lens). Only another section of the entire available illuminated field is used.